In the image information transmission apparatus such as facsimile transmission apparatus and the like, it has been the common practice to use a motor driven scanning element S for scanning a subject matter P to be transmitted through a line-circle conversion type optical fiber head H at a transmitter side as shown in FIG. 1 and a motor driven scanning element S for scanning a record sheet R through a multistylus head H at a receiver side as shown in FIG. 2. In this kind of image information transmission apparatus, there is a risk of the image being subjected to jitter by variation in speed of the motor M for driving the scanning elements S. In order to prevent the occurrence of such jitter, provision must be made of a multipolar motor having a sufficient margin for electric power and hence provision must be made of a special electric source.
The prior art technique of eliminating the influence of jitter upon the image information will now be described.
If the scanning element driving motor becomes irregular in rotation, it is impossible to know what number of the picture element bits from the left end of the picture surface is scanned by the scanning element. In order to know such picture element bit position, a clock pulse must be generated in correspondence with each picture element bit, the clock pulse being graduated in scale by angles which correspond to the rotary angles of the scanning element driving motor.
As means for generating such clock pulse, use may be made of a shaft encoder or a rotary encoder connected to the scanning element driving motor.
As seen from the above, if the image information is transmitted in parallel with the clock pulse, the influence of the jitter caused by the irregular rotation of the scanning element driving motor can be eliminated. Such parallel transmission of the image information and the clock pulse, however, is not compatible with the existing transmitter and receiver sets. In order to make the parallel transmission of the image information and the clock pulse compatible with the existing transmitter and receiver sets, provision must be made of means of making the intervals between the successive picture element bits of the image information, which correspond to the clock pulses whose intervals are different from each other, equal with each other, that is, provision must be made of means of making the intervals between the successive picture element bits of the image information correspondent to the clock pulses whose intervals are equal with each other. The use of the measures described ensures reception of the image information in the same manner as the process heretofore proposed.
As a result, provision must be made of means for correcting the signals whose intervals are different from each other to the signals whose intervals are equal with each other. For this purpose, the picture element bit signals whose intervals are different from each other are stored in a buffer memory and then these signals thus stored are read out by the clock pulses whose intervals are equal with each other so as to attain the above described purpose.
In FIG. 3 are shown graphs which illustrate the relation between the rotary angle of te motor for driving the scanning element for the optical fiber head at the transmitter side or the rotary angle of the motor for driving the scanning element for the multistylus head at the receiver side and the number of picture element bit. The above relation should preferably be straight line as shown by broken lines in FIG. 3. But, in practice the relation becomes non-rectilinear curve as shown by a full line curve in FIG. 3 owing to the irregular rotation of the scanning element driving motor. The shape of this curve becomes changeable in dependence not only with the number of poles of the motor, frequency of the electric source, stability of the voltage and the like but also with the load conditions. As shown in FIG. 3, let the maximum deviation of the curve from the ideal straight line be .DELTA.N bits, provision must be made of a buffer memory which can store n bits which are a little larger in number if compared with the maximum deviation .DELTA.N, but are much smaller in number if compared with the total number of bits in one line N. That is, the relation given by EQU .DELTA.N &lt; n &lt;&lt; N
must be satisfied.